Latching assemblies, and in particular magnetic latching assemblies, are in widespread use in modern aircraft for latching doors or closure panels on compartments containing oxygen equipment and masks and other emergency supplies for the passengers. In such magnetic latching assemblies, a permanent magnet is employed in maintaining the door in a closed or latched position and an electromagnet is used to cause the door to open or become in an unlatched position. Normally, the unlatching is accomplished by actuation of the electromagnet by the pilot of the aircraft. It has been found, however, that due to certain loading forces on the doors, the latching assemblies will either refuse to open when they are commanded to do so or will open automatically when they are not supposed to. These loading forces consist of flight loads due to twists of the airplane, vibration frequencies of different resonances between two mating parts, handling forces due to human causes, and gravitational loads caused by rapid aircraft acceleration or deceleration.
A latching assembly designed to overcome the above problems is shown in U.S. Pat. No. 3,635,511, entitled "Latching Assembly with Magnetic Latching", issued to H. A. Waller. In Waller, a first latching subassembly, including an electromagnet, is fastened to the inside surface of a compartment doorjamb and a second latching subassembly, including a latch lever and a permanent magnet latch bar mounted on the latch lever, is mounted adjacent the upper edge of the inside surface of the compartment door. When the latching assembly is closed, the permanent magnet mechanically engages the pole pieces of the first latching assembly and stays in position due to the magnetic attraction between itself and the metallic first latching assembly. Upon actuation of the electromagnet, the magnet and the latch to which it is coupled is repelled from the mechanical engagement and pivots out of latching position assisted by a spring. Thus, the permanent magnet both maintains or holds the latched position and acts as the mechanical latching engagement, until repelled by the electromagnet. Another latching assembly is shown in U.S. Pat. No. 3,860,277, entitled "Latching Assembly with Magnet Locking", issued to W. S. Wang. In a first embodiment of Wang, an electromagnet is positioned on the inside surface of a compartment top wall. A first latching lever, having a permanent magnet thereon, is pivotally mounted adjacent the electromagnet and coupled to the top wall. A second latch lever is mounted on a door and is biased open by a spring. The latch levers are held in mechanical engagement by the permanent magnet against the force of the bias spring. Upon activation of the electromagnet, the permanent magnet is repelled, causing the latch levers to unlatch. In a second embodiment, a spherical latch member or ball is held in mechanical engagement by a circumferentially spaced array of latch balls which are operable to engage the spherical latch member. A latch plunger which causes the latch balls to engage the spherical latch member is biased to a rearward unlatched position by a coil spring. The plunger is normally maintained in a forward latched position by means of a permanent magnet mounted on the plunger which attracts the poles of an electromagnet and overcomes the bias of the coil spring and a C-shaped spring which normally causes the latch balls to be in an expanded state. When the electromagnet is actuated, the force of the permanent magnet is overcome and the bias spring allows the latching assembly to unlatch.
Severe difficulties exist, however, with the latching assemblies of the above configurations. The door lever in Waller is directly loaded by the permanent magnet engaging the detent of the pole piece, causing a critical interface where the latch members meet with difficult tolerance controls. The inner latch members of Wang are also directly loaded by the permanent magnet, particularly in the first embodiment, again causing a critical interface where the latch members meet with difficult tolerance controls. It is apparent that poor quality control of the interfaces would inevitably lead to premature unlatching due to forces on the magnet or to lock-up due to excessive friction. In addition, in the second embodiment of Wang, any door loading would cause the spherical latch member to jam up against the latch balls and the latch plunger and prevent the electromagnet from unlatching the door since the bias spring is not strong enough to overcome the frictional forces between the spherical latch member, the latch balls and the latch plunger. Furthermore, any other types of loads on the door are directly transmitted to the permanent magnet, thereby increasing the probability of premature unlatchings.
Accordingly, it is a general object of the present invention to provide an improved latching assembly.
It is another object of the present invention to provide a latching assembly employing a permanent magnet which is not susceptible to premature unlatching or to lock-ups.
It is a further object of the present invention to provide a latching assembly which does not have critical interfaces.
It is still another object of the present invention to provide a latching assembly employing a permanent magnet in which the permanent magnet is disassociated from the latch members.